Ethanol for industrial use is conventionally produced from organic feed stocks, such as petroleum oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulosic materials, such as corn or sugar cane. Conventional methods for producing ethanol from organic feed stocks, as well as from cellulosic materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in organic feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulosic materials, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulosic materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. The reduction of various carboxylic acids over metal oxides has been proposed by EP 0175558 and U.S. Pat. No. 4,398,039. A summary of some of the developmental efforts for hydrogenation catalysts for conversion of various carboxylic acids is provided in Yokoyama, et al., “Carboxylic acids and derivatives” in: Fine Chemicals Through Heterogeneous Catalysis, 2001, 370-379.
U.S. Pat. No. 8,080,694, the entire contents and disclosures of which are hereby incorporated by reference, describes a process for hydrogenating alkanoic acids in the present of a catalyst comprising a platinum group metal, a metallic promoter, and a silicaceous support promoted with a redox promoter. U.S. patent application Ser. No. 13/179,955, the entire contents and disclosures of which are hereby incorporated by reference, describes a process for forming ethanol comprising hydrogenating acetic acid in the presence of a catalyst comprising platinum, tin and optionally a third metal on a support. U.S. Pat. No. 7,863,489, the entire contents and disclosures of which are hereby incorporated by reference, describes a process for the formation of ethanol by the hydrogenation of acetic acid in the presence of a catalyst consisting essentially of platinum and tin. U.S. patent application Ser. No. 12/588,727, the entire contents and disclosures of which are hereby incorporated by reference, describes processes for producing ethanol by the hydrogenation of acetic acid in the presence of a catalyst comprising or consisting essential of platinum and tin on a silicaceous support or a modified silicaceous support. U.S. patent application Ser. No. 12/698,947, the entire content and disclosures of which are hereby incorporated by reference, describes a process for producing ethanol by hydrogenating acetic acid in the presence of a catalyst comprising a first metal, a silicaceous support, and at least one support modifier.
U.S. Pat. No. 6,495,730 describes a process for hydrogenating carboxylic acid using a catalyst comprising activated carbon to support active metal species comprising ruthenium and tin. U.S. Pat. No. 6,204,417 describes another process for preparing aliphatic alcohols by hydrogenating aliphatic carboxylic acids or anhydrides or esters thereof or lactones in the presence of a catalyst comprising platinum and rhenium. U.S. Pat. No. 5,149,680 describes a process for the catalytic hydrogenation of carboxylic acids and their anhydrides to alcohols and/or esters in the presence of a catalyst containing a Group VIII metal, such as palladium, a metal capable of alloying with the Group VIII metal, and at least one of the metals rhenium, tungsten or molybdenum. U.S. Pat. No. 4,777,303 describes a process for the productions of alcohols by the hydrogenation of carboxylic acids in the presence of a catalyst that comprises a first component which is either molybdenum or tungsten and a second component which is a noble metal of Group VIII on a high surface area graphitized carbon support. U.S. Pat. No. 4,804,791 describes another process for the production of alcohols by the hydrogenation of carboxylic acids in the presence of a catalyst comprising a noble metal of Group VIII and rhenium. U.S. Pat. No. 4,517,391 describes preparing ethanol by hydrogenating acetic acid under superatmospheric pressure and at elevated temperatures by a process using a predominantly cobalt-containing catalyst.
Existing processes suffer from a variety of issues impeding commercial viability including: (i) catalysts without requisite selectivity to ethanol; (ii) catalysts which are possibly prohibitively expensive and/or nonselective for the formation of ethanol and that produce undesirable by-products; (iii) required operating temperatures and pressures which are excessive; and/or (iv) insufficient catalyst life.